The present invention relates to an electric welding gun comprising a device permitting indexing and de-indexing, which is to say the locking and the unlocking of the movement of the clamp, for example the rotation in the case of a clamp about X or the translation in the case of a clamp along J, relative to its support, for example an arm of a robot on which the clamp is mounted.
A welding cycle is comprised of three phases: approach, welding and disengagement. During the welding phase, a welding clamp must be able to undergo a movement for example opening and closing, relative to the robot so as to adapt to the plates to be assembled, in particular during approach which corresponds to the insertion and superposition of the two pieces to be welded between the electrodes and the clamp and the establishment of a stabilized force of the two electrodes creating an electric circuit.
Once welding is completed, the clamp is then opened and brought by the robot to another point where welding is to be carried out.
In the course of these movements, in particular to emplace the welding gun relative to the plates to be assembled, the movement of the clamp, which is open, can become troublesome and prevent a precise path and positioning of the assembly. Thus, so as to optimize the cycle time of the robot, the latter always move along two different axes at its maximum speed. Because of this, during given accelerations of the robot, the welding gun tends to oscillate.
Also, to avoid substantial inertial phenomena and to avoid the gun turning because of acceleration imparted by the robot, the movement of the assembly of the clamp is momentarily locked by an indexing system. Also, most of the welding clamps are provided with an index system having an influence on the clamp during its displacement from one work station to another, for example.
The electric motor-driven welding clamps generally used, have an indexing and de-indexing system constituted by a jack of which the extended position of the rod permits blocking the clamp and of which the retracted position of the rod frees the movement of the clamp so as to permit self-centering of the electrodes on a plate to be assembled during approach, and this without imparting force to the plates. So as to promote self-centering, the clamp comprises balancing springs permitting giving to the clamp a balanced position about its welding plane.
However, in the case of electric motorized welding clamps, the presence of the jack requires, in addition to the electric motor circuit of the clamp, the presence of a compressed air circuit as well as all the elements associated therewith, namely tubing, a compressor, etc.
It is thus necessary to provide two different types of supply.
The present invention accordingly seeks to overcome these drawbacks by providing an electric welding gun having an electric motorized welding clamp in which the locking and unlocking device of the movement of the welding clamp relative to the welding plane, does not need a pneumatic, hydraulic or other supply.
To this end, the present invention has for its object an electric welding gun having an electric motorized welding clamp comprising a fixed indexed arm and a movable arm, provided respectively with an electrode, as well as an indexing and de-indexing device locking and unlocking the movement of the clamp relative to the welding plane. The indexing and de-indexing device comprises mechanical means arranged to ensure locking and unlocking of the movement of the clamp, in the course of the opening/closing movements of the clamp, under the influence of electrical control means for opening and closing the clamp.
Because of this, at the end of a welding phase, during opening of the clamp by the electrical control means, the mechanical means act on the clamp so as to index it, while conversely, an actuation of the electrical control means in the direction of closing the clamp results in driving the mechanical means to de-index the clamp.
A welding gun according to the invention can thus have an X clamp as well as a J clamp.
In the case of an X clamp, according to a preferred embodiment, the mechanical means of the indexing and de-indexing device of the clamp are constituted by a cam, a rod and a roller, the cam being mounted rotatably about its axis of securement on an ear of the selected fixed arm of the clamp, the rod having one end mounted rotatably about its axis of connection with the cam, the connection axis being parallel to the axis of securement of the cam and spaced from the latter, and one end mounted rotatably about a drive trunnion whose longitudinal axis is also parallel to the axis of rotation of the cam, the drive trunnion being itself in sliding pivotal connection with the ear of the second arm of the required movable clamp, the roller being itself secured to the articulation of the clamp and adapted to coact with the profile of the cam.
Preferably, the roller is mounted, by means of a support of the indexing device, secured to the articulation of the clamp, the axis of the roller being parallel to the axis of securement of the cam, the roller being adapted to roll along the profile of the cam and the roller being moreover mounted slidably relative to its support, the sliding in translation being limited by resilient return means such as an elastomeric member.
The cam has a profile defined by different radii different diameters of the cam and, when the roller rolls along the greater diameter of the cam, the arms of the clamp having a movement of rotation about the articulation of the clamp, index themselves.
A welding gun according to the invention therefore has only a single electrical supply and it is thus not necessary to provide a pneumatic or hydraulic supply for the indexing and de-indexing device. There can thus also be omitted all the circuits and components concerned with another supply such as a pneumatic supply for example, the tubing, a compressor, etc.
Preferably, a welding gun according to the invention has moreover additional safety to the extent that, in the case of the absence of energy supply to the clamp, the clamp and in particular its indexing and de-indexing device remain in position and the clamp remains manually usable.
Moreover, there is obtained a welding gun in which the speed of indexing and de-indexing does not depend on the speed of a jack but on the speed of the electric motor actuating the clamp. Furthermore, the roller rolling on the cam leads to gentle indexing, in contrast to a jack, which is abrupt.